1. Field of the Invention
The present invention relates to a circulating fluidized bed reactor device comprising a reactor chamber delimited horizontally by walls, a centrifugal separator and a back pass for heat recovery, the reactor device comprising means for introducing a fluidizing gas into the reactor chamber and for maintaining a fluidized bed of particles in said chamber, means for transferring gas to be dedusted from the reactor chamber into the separator, means for discharging separated particles from the separator and means for transferring dedusted gas from the separator into the back pass, the latter having a common wall with the reactor chamber.
2. Discussion of Related Art
In general, a reactor device is a boiler device where fuel particles (to which sorbent particles are suitably added for sulfur capture) are burnt in the reactor chamber, also named furnace or combustion chamber, and where heat generated is recovered in the back pass, also named pass boiler, so as to produce energy (e.g. for driving electricity production turbines).
U.S. Pat. No. 4,745,884 discloses such a circulating fluidized bed reactor. In this reference, the reactor chamber and the back pass are contained within an upstanding, generally rectangular shaped waterwall structure. Therefore, the assembly of the reactor chamber and the back pass is compact.
However, U.S. Pat. No. 4,745,884 discloses the reactor comprising two separators, respectively disposed on each side of the structure containing the reactor chamber and the back pass and situated at a distance from said structure. These separators have generally circular cross sections and are connected to the reactor chamber and to the back pass by external ducts.
Consequently, despite the compact constitution of the reactor chamber and the back pass, the reactor is not compact due to the disposition of the separators.
An object for the present invention is to provide for a more compact reactor.
This object is achieved by the fact that the separator has a side wall which is common wall with a side wall of the back pass.
The back pass has two common walls: a common wall with the reactor chamber which is preferably a front wall of the back pass and a rear wall of the reactor, and a common wall with the separator, which is a side wall.
The disposition of the separator with the reactor chamber and the back pass is therefore much more compact than in U.S. Pat. No. 4,745,884. Further, as will be described herein-after, a more simple and compact constitution of the connections between the separator and the reactor chamber or the back pass can be achieved. In particular, the means for discharging dedusted gas from the separator to the back pass can comprise one or several openings formed in a side wall of the back pass which is an upper extension of the common wall between the separator and the back pass.
With respect of the prior art, the compact reactor device of the invention has an increased number of common walls between the enclosures of the reactor chamber, the separator and the back pass. The pressures in these enclosures are different from the outside pressure. As a consequence, the walls of these three enclosures are pressure parts that must be strong enough to endure pressure differentials, which involves that these walls are expensive to manufacture and need adapted stiffening means. By increasing the number of common walls, the invention limits the number of such pressure parts and of stiffening means which is advantageous as to costs and ease of manufacture.
The back pass and the means for transferring dedusted gas from the separator into said back pass (e.g. a flue gas plenum) can also have a wall in common that can be a vertical extension of the common wall between the back pass and the separator. The reactor device can also comprise a heat exchanger area, located under the back pass and having a common wall therewith.
The back pass has heat recovery elements with heat exchanging surfaces extending therein. These heat recovery elements can be supported by supports that extend from side to side inside the back pass and that are also used as stiffening means for the walls of the back pass. Such stiffening means are much easier to arrange in the back pass than in the reactor chamber or in the separator because the mixture of gas and particles that circulates in the reactor chamber and in the separator is very aggressive as far as erosion is concerned, whereas the dedusted gas that circulates in the back pass is much less aggressive. With the invention, the common wall between the separator and the back pass, as well as the common wall between the reactor chamber and the back pass, can easily be stiffened by the stiffening means arranged in the back pass, without it being compulsory to foresee specific stiffening means for the concerned wall of the separator.
Advantageously, the device comprises at least one stiffened wall that extends between two supporting walls and that is stiffened by stiffening means comprising a truss beam extending along said stiffened wall and having respective ends that are respectively fastened to one of said supporting walls.
With such stiffening means, only a limited quantity of material is required for stiffening the stiffened wall. They are located along said wall so that they do not significantly disturb the hot flow of gas and/or of gas and particles in the enclosure where they are accommodated. For the reasons explained above, said enclosure is advantageously the back pass.
Although any wall of the reactor device can be stiffened by such stiffening means, these stiffening means are particularly advantageous for stiffening an xe2x80x9cinternalxe2x80x9d wall of the reactor device that is, for example, a common wall between the reactor chamber and the back pass, or a common wall between the back pass and the separator. Generally, the stiffened wall has to bear without buckling a significant pressure gradient between its two faces.
The ends of the truss beam are attached to the supporting walls close to the stiffened wall so that little temperature gradient occurs between the stiffened wall and the attaching places for the ends of the truss beam to the supporting walls, so that the stiffening means are subject to little temperature gradient.
Furthermore, the temperature gradient that applies to the stiffened wall is oriented perpendicularly to said wall and, as a reaction to said gradient, said wall tends to expand or contract in its own direction, that is in the direction of the truss beam. Therefore, the truss beam does not oppose to the expansion or contraction stresses but it prevents that these stresses lead to the stiffened wall being buckled.
Advantageously, the truss beam is attached to the stiffened wall by attaching means allowing a relative sliding between said beam and said wall.
Advantageously, the truss beam is composed of at least a first elongate beam member located against said stiffened wall, a second elongate beam member parallel to said first beam member and spaced therefrom, and a plurality of spacing members, defining spaces between them and connecting said first and second elongate beam members.
In this case, the truss beam has a trellis work structure, which is relatively light despite offering a high mechanical resistance to stresses and which causes very little disturbance to the flow of gas and/or of gas and particles in the enclosure where the truss beam is located. The use of such a trellis work structure avoids that particles or ashes accumulate thereon, and the trellis work structure does not have a significant effect on the heat transfer in the heat exchangers.
Advantageously, the truss beam has a tube structure formed of tubes allowing a circulation of a heat transfer medium therein.
Depending on the location of the truss beam, the heat transfer medium can be water and/or steam. When the stiffened wall is one of the back pass walls, said tube structure can be connected to the heat exchangers situated in the back pass, so that the same heat transfer medium circulates in the tube structure and in the heat exchangers.
When the reactor device has walls provided with heat exchange tubes, it is also possible, whatever the location of the stiffened wall, that said tube structure of the truss beam be connected to said heat exchange tubes so that the same heat transfer medium circulates therein. The truss beam being generally subject to a high temperature, the use of a tube structure with circulation of a heat transfer medium therein is particularly advantageous.
Advantageously, the common walls are planar walls. It is also an advantage that they form between them a substantially right angle.
This enables a easier and more efficient stiffening of the common walls.
Advantageously, the common wall between the back pass and the reactor chamber is the front wall of the back pass, and the separator has a front wall disposed as an extension of said front wall of the back pass.
The fact that the front wall of the separator is aligned with the front wall of the back pass also facilitates the stiffening of these aligned front walls by means of the same rectilinear stiffeners.
All the same, the stiffening of the reactor chamber walls and of the external walls of the separator(s) is facilitated since the loads due to inside pressure are transferred by corners attachment directly through a continuous straight wall.
The presence of common walls enables that expansion joints be avoided. For example, an expansion joint between the reactor chamber, the means for transferring gas to be dedusted to the separator(s) (e.g. an acceleration duct) and the separator can be avoided, as well as can be an expansion joint between the separator(s), the means for transferring dedusted gas to the back pass (e.g. a flue gas plenum) and the back pass. When the reactor device comprises one or several heat exchanger areas located under the back pass and having a common wall therewith, expansion joints can be avoided between the heat exchanger area(s), the reactor chamber and the return duct(s) conveying separated particles into said area(s).
The compact reactor device of the invention can have a reduced content of refractory materials with respect to the prior art; where required, the reactor device walls can have thin refractory layers, instead of thick refractory layers as in the prior art.
Globally, with the above features, a compact and rigid structure is obtained at rather low costs.
In an advantageous embodiment, the separator has a rear wall disposed as an extension of the rear wall of the back pass, opposed to said front wall thereof.
When the front and rear walls of the separator extend as respective extensions of the front and rear walls of the back pass while they are aligned therewith, then the separator and the back pass can present, when considered together, a generally rectangular cross section. Further, the reactor chamber can also present a rectangular cross section. The combination of these two rectangular cross sections achieves a very compact assembly.
Advantageously, the side wall which is common between the separator and the back pass is disposed as an extension of a side wall of the reactor chamber.
In one embodiment, the means for transferring gas to be dedusted from the reactor chamber into the separator comprise an acceleration duct which extends between a wall of the reactor chamber in which an outlet for gas to be dedusted (that is a mixture of gas and particles) is formed and a wall of the separator in which an inlet for gas to be dedusted is formed, said acceleration duct having a cross section which decreases in a direction going from said outlet to said inlet.
In this embodiment, the invention both provides for a very compact structure of the reactor and for a more efficient separation of the particles with respect to the fluidization gas since the mixture of gas and particles enters the separator at rather high speed, which reinforces the efficiency of the centrifugal separation carried out in the separator.
Thus, advantageously, the wall of the reactor chamber in which said outlet is formed is a side wall of said chamber and the separator wall in which said inlet is formed is a front wall of the separator.
In another embodiment, the reactor chamber has a wall portion, that extends as an extension of said common wall between the reactor chamber and the back pass and that is common to a wall portion of the separator, an opening enabling gas to be dedusted to circulate from the chamber to the separator being formed in said common wall portion.
In this other embodiment, a more direct connection between the reactor chamber and the separator is achieved at low costs, since no external acceleration duct is necessary.
Advantageously, the reactor device can be top supported or else bottom supported. The latter possibility results from the compactness of the reactor device and of a possible location of its various components so that its center of gravity be low.